Where do I refill it with oil? Can I just put oil on the big hose that leads to the compressor? or do I have to pull-down the compressor again and add oil through the two holes where the hoses attach to?

You first pull a vacuum for 30 min. and then hold it for 10. If it looses less than 2 inches of merc, you fill it through the port on the low pressure hose (big hose on top). Then add your refrigerant.